There are four dorsal interossei. They lie in the intervals between the |metacarpal bones| and are bipenniform muscles (originate in two places). Each muscle originates from the adjacent sides of the |metacarpal bones| and are inserted in the base of the first phlanges. The first dorsal interossei is the largest of the four interossei. It is located on the back of the hand in the V-shaped interval between the |metacarpal bones| of the thumb, where it originates, and the first phlanges of the index finger, where it is inserted on the radial side. The second and third dorsal interossei are inserted into the middle finger with the second on its radial side and the third on its ulnar side. The fourth dorsal interossei is inserted into the ulnar side of the ring finger. These four muscles flex and extend the fingers.
